Proposed by Seednet, a member of TWNIC IP working group
The prosperous development of the broadband technology as well as the mobile communications leads to a predictable all-time high demand of IP addresses. As the IPv6 implementation just moved out of experimental phase and has not been widely deployed, IPv4 addresses are considered much more cost-effective for ISPs to cope with the rapid expansion of their network, despite of the fact that IPv4 support will be short soon. It is a challenging task for Internet Registries to allocate IP addresses conservatively and fairly while supporting sufficient IP addresses for those who really need them.
To justify ISPs' request, Internet Registries need to have relevant knowledge of the technology and the idea of where assigned IP addresses go. This proposal presents general guidelines of IP address assignment for broadband Internet connections currently undertaken by Seednet, the second largest ISP in Taiwan.
Broadband technologies like ADSL and Cable modem are similar in terms of the IP address requirement. Customers are typically categorized by the way their IP address assigned. Residential subscribers normally connect to the Internet provided dynamically assigned IP addresses whereas professional and business subscribers use static IP addresses to provide services for the incoming request from the Internet.
In the case of ADSL, the demand of IP Address comes from two parts – for ADSL network infrastructure and for subscribers' equipments such as the ATU-R and the PC. Comparing to the amount of IP addresses consumed by the subscribers' equipments, the IP address consumption for the ADSL network infrastructure is small.
Published by TWNIC on May 01, 2000, an ADSL assignment policy, which was agreed by major ADSL operators, classified users by the type of subscribers – home users and corporate users. For home users, no more than one static IP address was permitted while corporate users could have multiple IP addresses based on the needs. A few months later after, the policy of one IP restriction for home users was criticized. Many professional home users or SOHO complained and claimed their legitimacy of having more than one IP address for research or business purpose. On Oct 01, 2001, a revised ADSL assignment policy was released and has been applied thereafter. Instead of home and business type of users, the subscribers in the new policy are categorized into 3 types:
Residential ADSL service Subscribers are mainly home users. The ATU-R works in the bridge mode and one IP address (/32) is required and dynamically assigned for the CPE (Customer Premise Equipment). Statistic from ISP has shown that customer-to-IP ratio changes over time and is inconsistent among different ISPs.
Professional ADSL service Subscribers are professional home users or SOHO. The ATU-R works in the bridge mode and one IP address (/32) is required and statically assigned for the subscriber's PC.
Business ADSL service Subscribers are mainly small business users. The ATU-R works in the routing mode. For transmission speed of 64k/512k or less, each subscriber is statically assigned no more than 8 IP addresses. For those with higher speed, a number of 8 to 32 IP addresses (/29 to /27) can be assigned according to the subscriber's need. Since there are overheads of two IP addresses as the ATU-R works in the routing mode, it is possible but not economical for ISPs to assign any number of IP addresses between 1 and 8.
Like that of ADSL, demand of IP Address comes from two parts – for cable network infrastructure such as CMTS and cable modem and for CPE. At the meantime, there is no explicit policy available for ISPs to follow. TWNIC will soon produce a policy draft and invite ISPs' opinions.
There are two types of services commonly implemented in Taiwan:
Telco-Return service One-way service realizes downstream traffic by cable modem link and upstream traffic by general traditional dail-up connection. Three IP addresses are required; one for the cable modem, one for the dial-up modem's PPP session, and one for the CPE. The IP address for the cable modem can be private whereas the other two need to be public.
Two-way service In this case both downstream and upstream traffics are realized through the cable modem link. Since there is no dial-up service required, one private for cable modem and one public IP address for CPE are sufficient.
Currently all IP addresses are dynamically assigned for both service types. However, there is a demand of static IP addressing in the market coming from potential business and professional users. TWNIC tends to reference the existing ADSL IP address assignment policy with minimum modifications for Cable modem. The policy will need to be tailored to accommodate the complex structure of cable modem service.
A concern has been raised regarding the IP address consumption of residential subscribers. One dynamic IP address is allocated for ADSL subscriber per each PPPoE request or for Cable modem subscriber per each DHCP request. As it is more and more common for residential users to have more than one CPE, it is very likely to see more than one PPPoE or DHCP session requested by the same subscriber. The customer-to-IP ratio has been decreased from 3:1, 2:1, to current 1.2:1. It is likely that the ratio would reach 1:1 or even less.